A welding method for 9Cr-1Mo steel and 20MnMo steel

Abstract

This invention discloses a welding method for 9Cr-1Mo steel and 20MnMo steel. The welding method includes the following steps: S1, overlaying a transition layer; S2, cutting the transition layer; S3, machining the bevel of the transition layer side; and S4, butt-jointing the transition layer with the 20MnMo steel side. This welding method for 9Cr-1Mo steel and 20MnMo steel solves the problem of difficult welding of these two steels. Using alloy steel as the transition layer reduces welding costs, simplifies welding difficulty, and improves production efficiency.

Description

Technical Field

[0001] This invention relates to the field of welding processing technology, and in particular to a welding method for 9Cr-1Mo steel and 20MnMo steel. Background Technology

[0002] 9Cr-1Mo steel, including T91 / P91 / F91 / Gr91 / 10Cr9Mo1VNb steel, possesses excellent high-temperature stability and is commonly used in large power plant boilers and other applications. 20MnMo steel is a low-carbon quenched and tempered steel. It is commonly used in the manufacture of medium-temperature thick-walled pressure vessels and important forgings.

[0003] 9Cr-1Mo steel and 20MnMo steel differ significantly in chemical composition and mechanical properties, and have different welding characteristics. Their stress-relief welding heat treatment temperature ranges do not overlap, making it impossible to formulate a heat treatment process that can simultaneously meet the requirements of both materials. Therefore, 9Cr-1Mo steel and 20MnMo steel cannot be directly welded. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention designs a welding method for 9Cr-1Mo steel and 20MnMo steel.

[0005] The present invention adopts the following technical solution:

[0006] A welding method for 9Cr-1Mo steel and 20MnMo steel, comprising the following steps:

[0007] S1. Weld Overlay Transition Layer: The 9Cr-1Mo steel side bevel is machined, and the bevel and surrounding base material are cleaned and ground. Anhydrous ethanol is used for cleaning. Non-destructive testing (NDT) is performed on the bevel and surrounding area. After passing NDT, pre-assembly is performed, followed by spot welding of the backing and fixing blocks after preheating. The spot welds are visually inspected and ground until a smooth transition with the surrounding base material is achieved. After preheating, submerged arc welding is used until the bevel is filled and a smooth transition with the surrounding base material is achieved. Immediately after welding, the material is placed in a furnace for hydrogen removal. It is then held at room temperature and slowly cooled. The backing is removed by machining. NDT is performed. After passing NDT, post-weld heat treatment is conducted. NDT is then performed again after post-weld heat treatment.

[0008] S2. Cutting the transition layer: After passing the non-destructive testing and re-exploration, cut along the center of the butt weld.

[0009] S3. Machining the side bevel of the transition layer: The side bevel of the transition layer is machined.

[0010] S4. Butt joint between the transition layer and the 20MnMo steel side: The 20MnMo steel side is beveled using mechanical processing. The bevel and the surrounding base material are cleaned and ground. Anhydrous ethanol is used for cleaning. Non-destructive testing is performed on the bevel and the surrounding area. After passing the non-destructive testing, pre-assembly is performed. After preheating, spot welding and fixing blocks are installed. The spot welds are visually inspected and ground to ensure a smooth transition with the surrounding base material. After preheating, manual argon arc welding is used for the root pass, manual electric arc welding for the transition pass, and submerged arc welding for the cover pass pass. Welding continues until the bevel is filled and smoothly transitions with the surrounding base material. The weld is immediately placed in a furnace for hydrogen removal. Aluminum silicate fiber insulation is used for ring cooling to room temperature. After passing the non-destructive testing, post-weld heat treatment is performed. Non-destructive testing is performed again after post-weld heat treatment.

[0011] Preferably, in step S1, the preheating temperature during the entire process of transition layer welding is not lower than 205°C, and in step S4, the preheating temperature during the entire process of transition layer welding is not lower than 180°C.

[0012] Preferably, in steps S1 and S4, the hydrogen removal parameters after the transition layer overlay welding are: hydrogen removal temperature 250~350℃, heat preservation time 2.5~3h, and after the heat preservation is completed, aluminum silicate fiber is used for wrapping and slow cooling.

[0013] Preferably, in step S1, the heat treatment parameters after the transition layer is weld overlay are a heat treatment temperature of 750℃±15℃ and a holding time of 7.5h; in step S4, the heat treatment parameters after the transition layer is weld overlay are a heat treatment temperature of 620℃±15℃ and a holding time of 8h.

[0014] Preferably, in steps S1 and S4, the welding joint is a butt joint.

[0015] Preferably, in steps S1 and S4, the bevel and the surrounding base material within a range of not less than 20mm are cleaned and polished.

[0016] Preferably, in steps S1 and S4, non-destructive surface testing is performed on the bevel and the surrounding area within a range of not less than 20mm.

[0017] Preferably, in step S1, the gap at the root of the bevel is ensured to be ≥40mm during pre-assembly.

[0018] Preferably, in step S4, the gap at the root of the bevel is 2-3 mm during pre-assembly.

[0019] Preferably, in step S3, the thickness of the transition layer must be at least 6 mm.

[0020] The beneficial effects of this invention are: it solves the problem of difficult welding between 9Cr-1Mo steel and 20MnMo steel. Using alloy steel as a transition layer reduces welding costs, simplifies welding difficulty, and improves production efficiency. Attached Figure Description

[0021] Picture 1 This is a schematic diagram of a weld overlay transition layer in Embodiment 1 of the present invention;

[0022] Picture 2 This is a schematic diagram of a cutting transition layer in Embodiment 1 of the present invention;

[0023] Picture 3 This is a schematic diagram of a side bevel of the machining transition layer in Embodiment 1 of the present invention;

[0024] Picture 4 This is a schematic diagram of a welding transition layer and 20MnMo steel in Embodiment 1 of the present invention;

[0025] In the figure: 1. 9Cr-1Mo steel, 2. Transition layer overlay weld, 3. Transition layer cutting position, 4. Transition layer, 5. 20MnMo steel, 6. Butt weld between transition layer and 20MnMo steel. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below through specific embodiments and in conjunction with the accompanying drawings:

[0027] Example 1: A welding method for 9Cr-1Mo steel and 20MnMo steel, the welding method steps are as follows:

[0028] S1, weld overlay transition layer: such as Picture 1 As shown, the 9Cr-1Mo steel bevel on one side is machined using a 12° V-groove. Submerged arc welding is used, and the weld joint is a butt joint. The bevel and the surrounding base material within a 20mm radius are cleaned and ground; anhydrous ethanol is used for cleaning; non-destructive testing (NDT) is performed on the bevel and the surrounding 20mm radius; after passing the NDT, pre-assembly is performed, ensuring a bevel root gap ≥40mm. The backing, fixing blocks, and other accessories are tack welded at a preheated temperature above 205℃; the tack welds are visually inspected and ground to a smooth transition with the surrounding base material; submerged arc welding is then performed at a preheated temperature above 205℃. The weld bevel is filled and smoothly transitioned to the surrounding base material; a transition layer is formed by overlaying weld 2. Immediately after welding, the weld is placed in a furnace for hydrogen removal. The hydrogen removal parameters are: hydrogen removal temperature 250~350℃, holding time 2.5~3h; after holding, aluminum silicate fiber is used for insulation and slow cooling to room temperature; the backing is removed by machining; non-destructive testing is performed; after passing the non-destructive testing, post-weld heat treatment is performed. The heat treatment parameters are: heat treatment temperature 750℃±15℃, holding time 7.5h; after post-weld side treatment, non-destructive testing is performed again.

[0029] S2, Cutting the transition layer: such as Picture 2As shown, after passing the non-destructive testing, the transition layer cutting position 3 along the center of the butt weld is cut open by mechanical processing.

[0030] S3, Machining transition layer side bevel: such as Picture 3 As shown, the bevel is machined using mechanical processing, with a U-shaped bevel and a blunt edge of 2mm; the thickness of the transition layer 4 must be no less than 6mm.

[0031] S4, Transition layer and 20MnMo steel side connection: (e.g.) Picture 4 As shown, the welding method for the transition layer and the 20MnMo steel side is argon arc welding + manual arc welding + submerged arc welding; the welding joint type is butt joint; the 20MnMo steel is machined on all five sides using a U-shaped bevel with a 2mm blunt edge; the bevel and the surrounding base material within a range of not less than 20mm are cleaned and ground; anhydrous ethanol is used for cleaning; the bevel and the surrounding area within a range of not less than 20mm are subjected to non-destructive testing; after passing the non-destructive testing, pre-assembly is performed, ensuring a 2-3mm gap at the root of the bevel, and the preheating temperature is not lower than 180℃ before spot welding and assembling accessories such as fixing blocks; spot welding... The weld is visually inspected and ground until it smoothly transitions with the surrounding base material. After preheating to a temperature not lower than 180℃, manual argon arc welding is used for the root pass, manual electric arc welding for the transition pass, and submerged arc welding for the cover pass. Welding continues until the bevel is filled and smoothly transitions with the surrounding base material, forming a transition layer and butt weld 6 with 20MnMo steel. Immediately after welding, the weld is placed in a furnace for hydrogen removal. The hydrogen removal parameters are: hydrogen removal temperature 250~350℃, holding time 2.5~3h. Aluminum silicate fiber insulation is used for ring cooling to room temperature. After passing non-destructive testing, post-weld heat treatment is performed. The post-weld heat treatment parameters are: heat treatment temperature 620℃±15℃, holding time 8h. Non-destructive testing is performed again after post-weld heat treatment.

[0032] Welding performance tests were conducted on 9Cr-1Mo steel and 20MnMo using Example 1; the test results are as follows:

[0033] The chemical composition (%) of the transition layer cladding metal is as follows, expressed as a percentage by mass:

[0034] C Si Mn Cr Mo Ni Cu V P S Fe 0.058 0.39 0.66 1.04 0.48 0.02 0.04 0.19 0.012 0.004 --

[0035] The chemical composition (%) of the cladding metal of the transition layer and the butt weld of 20MnMo steel is as follows, with the chemical composition expressed as a percentage by mass:

[0036] C Si Mn Cr Mo Ni Cu V P S Fe 0.06 0.08 1.63 0.63 0.45 1.52 0.08 0.10 0.006 0.004 --

[0037] The chemical composition (%) of the transition layer cladding metal required for actual production and use is as follows, with the chemical composition expressed as a percentage by mass:

[0038] C Si Mn Cr Mo Ni Cu V P S Fe Max.0.10 0.15~0.35 0.40~0.70 1.00~1.30 0.50~0.70 Max.0.30 Max.0.20 0.15~0.35 Max.0.020 Max.0.015 --

[0039] The chemical composition (%) of the cladding metal of the transition layer and the butt weld of 20MnMo steel is as follows, with the chemical composition expressed as a percentage by mass:

[0040] C Si Mn Mo Ni P S Fe Max.0.12 Max.0.60 0.40~0.70 0.25~0.45 Max.0.90 Max.0.020 Max.0.015 --

[0041] The above data proves that the welding performance of 9Cr-1Mo steel and 20MnMo in this experiment meets the requirements for production and use.

[0042] Example 2: The difference between this example and Example 1 is that the side beveling of the 9Cr-1Mo steel is processed by hot cutting followed by machining. Everything else is the same as in Example 1.

[0043] Example 3: The difference between this example and Example 1 is that the cutting method after the transition layer is weld overlay is thermal cutting followed by machining. Everything else is the same as in Example 1.

[0044] Example 4: The difference between this example and Example 1 is that the transition layer beveling method is thermal cutting followed by machining. Everything else is the same as in Example 1.

[0045] Example 5: The difference between this example and Example 1 is that the side beveling of the 20MnMo steel is processed by thermal cutting followed by machining. Everything else is the same as in Example 1.

[0046] Example 6: The difference between this example and Example 1 is that the 9Cr-1Mo steel side bevel uses a Type I bevel. Everything else is the same as in Example 1.

[0047] Example 7: The difference between this example and Example 1 is that a V-shaped bevel with a 2mm blunt edge is selected for the transition layer side bevel. Everything else is the same as in Example 1.

[0048] Example 8: The difference between this example and Example 1 is that the transition layer side bevel is an X-shaped bevel with a 2mm blunt edge. Everything else is the same as in Example 1.

[0049] Example 9: The difference between this example and Example 1 is that a V-shaped bevel with a 2mm blunt edge is selected for the 20MnMo steel side bevel. Everything else is the same as in Example 1.

[0050] Example 10: The difference between this example and Example 1 is that the 20MnMo steel side bevel is an X-shaped bevel with a 2mm blunt edge. Everything else is the same as in Example 1.

[0051] Example 11: The difference between this example and Example 1 is that the side beveling of the 9Cr-1Mo steel is processed by hot cutting followed by machining. Everything else is the same as in Example 1.

[0052] Example 12: The difference between this example and Example 1 is that the cutting method after the transition layer is weld overlay is thermal cutting followed by machining. Everything else is the same as in Example 1.

[0053] Example 13: The difference between this example and Example 1 is that the transition layer beveling method is thermal cutting followed by machining. Everything else is the same as in Example 1.

[0054] Example 14: The difference between this example and Example 1 is that the side beveling of the 20MnMo steel is processed by hot cutting followed by machining. Everything else is the same as in Example 1.

[0055] Example 15: The difference between this example and Example 1 is that the 9Cr-1Mo steel side bevel uses a Type I bevel. Everything else is the same as in Example 1.

[0056] Example 16: The difference between this example and Example 1 is that a V-shaped bevel with a 2mm blunt edge is selected for the transition layer side bevel. Everything else is the same as in Example 1.

[0057] Example 17: The difference between this example and Example 1 is that the transition layer side bevel is an X-shaped bevel with a 2mm blunt edge. Everything else is the same as in Example 1.

[0058] Example 18: The difference between this example and Example 1 is that a V-shaped bevel with a 2mm blunt edge is selected for the 20MnMo steel side bevel. Everything else is the same as in Example 1.

[0059] Example 19: The difference between this example and Example 1 is that the 20MnMo steel side bevel is an X-shaped bevel with a 2mm blunt edge. Everything else is the same as in Example 1.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A welding method for 9Cr-1Mo steel and 20MnMo steel, characterized in that, The welding method steps are as follows: S1. Welding transition layer: The side bevel of 9Cr-1Mo steel is machined by mechanical processing. The bevel and the surrounding base material are cleaned and ground. Anhydrous ethanol is used for cleaning. Non-destructive testing is performed on the surface of the bevel and the surrounding area. After the surface non-destructive testing is qualified, pre-assembly is carried out. After preheating, the backing and fixing blocks are spot welded. Visually inspect the spot welds and grind them until they smoothly transition with the surrounding base material; after preheating, use submerged arc welding to weld until the bevel is filled and smoothly transitions with the surrounding base material; immediately after welding, put the welds into the furnace for hydrogen removal; hold them at the temperature and cool them slowly to room temperature; machine to remove the backing; perform non-destructive testing; after passing the non-destructive testing, perform post-weld heat treatment; and perform a second non-destructive testing after the post-weld heat treatment. S2. Cutting the transition layer: After passing the non-destructive testing and re-exploration, cut along the center of the butt weld. S3. Machining the side bevel of the transition layer: The side bevel of the transition layer is machined. S4. Butt joint between the transition layer and the 20MnMo steel side: The 20MnMo steel side is beveled using mechanical processing. The bevel and the surrounding base material are cleaned and ground. Anhydrous ethanol is used for cleaning. Non-destructive testing is performed on the bevel and surrounding area. After passing the non-destructive testing, pre-assembly is performed. After preheating, spot welding and fixing blocks are installed. The spot welds are visually inspected and ground to ensure a smooth transition with the surrounding base material. After preheating, manual argon arc welding is used for the root pass, manual electric arc welding for the transition pass, and submerged arc welding for the cover pass. Welding continues until the bevel is filled and smoothly transitions with the surrounding base material. The weld is immediately placed in a furnace for hydrogen removal. Aluminum silicate fiber insulation is used for ring cooling to room temperature. After passing the non-destructive testing, post-weld heat treatment is performed. Non-destructive testing is performed again after post-weld heat treatment. In step S1, the chemical composition of the cladding metal in the transition layer, by mass percentage, is: C≤0.10%, Si 0.15%-0.35%, Mn 0.40%-0.70%, Cr 1.00%-1.30%, Mo 0.50%-0.70%, Ni≤0.30%, Cu≤0.20%, V 0.15%-0.35%, P≤0.020%, S≤0.015%, with the remainder being Fe; In step S4, the chemical composition of the cladding metal of the transition layer and the butt weld of 20MnMo steel, by mass percentage, is: C≤0.12%, Si≤0.60%, Mn 0.40%-0.70%, Mo 0.25%-0.45%, Ni≤0.90%, P≤0.020%, S≤0.015%, with the remainder being Fe; In step S1, the preheating temperature during the entire process of transition layer welding is not lower than 205°C; in step S4, the preheating temperature during the entire process of transition layer welding is not lower than 180°C. In steps S1 and S4, the hydrogen removal parameters after the transition layer overlay welding are: hydrogen removal temperature 250~350℃, heat preservation time 2.5~3h, and after the heat preservation is completed, aluminum silicate fiber is used for heat preservation and slow cooling. In step S1, the heat treatment parameters after the transition layer is weld overlay are a heat treatment temperature of 750℃±15℃ and a holding time of 7.5h. In step S4, the heat treatment parameters after the transition layer is weld overlay are a heat treatment temperature of 620℃±15℃ and a holding time of 8h. In step S1, during pre-assembly, ensure that the gap at the root of the bevel is ≥40mm; In step S4, during pre-assembly, ensure that the gap at the root of the bevel is 2~3mm; In step S3, the thickness of the transition layer must be at least 6 mm.

2. The welding method for 9Cr-1Mo steel and 20MnMo steel according to claim 1, characterized in that, In steps S1 and S4, the welding joint is a butt joint.

3. The welding method for 9Cr-1Mo steel and 20MnMo steel according to claim 1, characterized in that, In steps S1 and S4, the bevel and the surrounding base material within a range of no less than 20mm are cleaned and polished.

4. The welding method for 9Cr-1Mo steel and 20MnMo steel according to claim 1, characterized in that, In steps S1 and S4, non-destructive testing is performed on the bevel and the surrounding area within a range of not less than 20mm.

Images